The Light-emitting Diode Is A Special Kind Of Diode

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LED production

Principle

The light-emitting diode is a special kind of diode. And ordinary diode, light emitting diode composed of a semiconductor wafer, these semiconductor materials previously passed through implantation or doping process to produce a pn junction structure. And the other diode, the current in the light emitting diode can be easily from the p electrode (anode) flow to the n electrode (anode), while the opposite direction. Two different carriers: the holes and electrons in the type of electrode voltage under the action of flow from the electrode to the pn junction. When the hole and electron meet complex, electrons drop to a lower energy level, while the photon energy is released.

The emitted wavelength of light, and its color is determined by the bandgap energy of the semiconductor material composed of a pn junction. Because silicon and germanium are indirect band gap materials, composite non-radiative transition of electrons and holes in these materials, such transition did not release photons, silicon and germanium diodes can not emit light. The material used in the light emitting diode is directly forbidden band type bandgap energy corresponding to the near-infrared, visible, or near ultraviolet region light energy.

The following is a traditional light emitting diode used in an inorganic semiconductor material and the light emitting color:

The majority of the white LED is currently in production by the covering layer of a pale yellow fluorescent powder coating made on Blu-ray LED (near-UV wavelength of 450 nm to 470 nm), such a yellow phosphor is usually doped with cerium yttrium – aluminum – gallium (Ce3 +: YAG) crystal ground into a powder mixed in a dense adhesive made. When the LED chip emits blue light, part of the Blu-ray will be this crystal is efficiently converted into a spectrum spectral center wide (about 580 nm) mainly yellow light. (In fact, a single crystal of Ce-doped YAG is regarded as more than phosphor scintillator.) Yellow light will stimulate the naked eye red and green receptors, and then mixing the blue light of the LED itself, making it look like a white light its color is often referred to as a “moonlight white”. This method of production of white LED by Nichia Corporation developed and used in the production of white LED since 1996. To adjust the pale yellow color of the light, the availability of other rare earth metal terbium or gadolinium substituted Ce3 +: YAG incorporating cerium (Ce), can even be done in order to part or all of the substituted YAG aluminum.

Based on the spectral characteristics of the object of red and green LED irradiation will look less than wide spectrum light source so distinctive.

In addition, due to the fluctuations of the production process, the finished color temperature of the LED is not uniform, from a yellow warm to cold blue has, in the production process for its out feature to make a distinction.

Another production method of the white LED is a bit like a fluorescent lamp, issued by the near ultraviolet LED is coated with a mixture of two phosphors, one is red light and blue light europium, another green-doped the zinc sulfide (ZnS), copper and aluminum. Metamorphism of the ultraviolet light causes the adhesive epoxy resin cracking is difficult to produce, and the shorter life. Compared with the first method, it is a lower efficiency and generate more heat (because of the large Stokes shift former), but the benefits are better spectral characteristics of light generated Attractive. Due to the higher power of UV LED efficiency, although the first method, brightness comparable out.

Last one method of manufacturing a white LED is not reuse the phosphor. The new approach is ZnSe epitaxial layer grown zinc selenide (ZnSe) substrate. Active zone when energized emits blue light the substrate yellow light, the mix is ??white light.

Other colors

Recently developed LED colors include pink and purple, and are covered in blue LED on one or two layers of phosphor caused. The pink red LED with a first layer of phosphorescent physical yellow-issued orange or red light and the second layer. Phosphor purple LED lights up orange. Some pink LED manufacturing method, there are some problems, e.g. some pink LED is a blue LED coated with fluorescent paint or polish, but they have the opportunity to spalling; while others spend white LED plus red phosphor powder body or dye, but in a short period of time the color will fade.

Price, ultraviolet, blue, pure green, white, pink and purple LED is more red, orange, green, yellow, infrared LED expensive, the former commercial use inferior.

The light emitting diodes are encapsulated in a plastic lens is more sturdy than the use of a glass bulb or fluorescent. Sometimes the outer package will be colored, but this is only for decoration or to increase the contrast, in essence, does not change the color of the light-emitting diode light-emitting.